Understanding the disease progression of abnormal hoof anatomy, Part 1

By looking at a standard or digital radiograph (note: digital radiographs are generally not true to size, so you will need to adjust your images to 100 percent true image), you can see and measure abnormalities of the horn-laminar zone (HLZ), digital alignment, palmar angle, SDT, the sole depth at the wing of P3 (SDW) and extensor process-coronary band (EP/CB) (Figure 1).

Grade I

Figure 2: Grade I laminitis. (Photos courtesy of Dr. Floyd)

The Grade I laminitis foot is considered pathologic when it has a palmar angle of 5 to 9 degrees (Figure 2). In the lower palmar angle (PA) cases of Grade I (e.g., 5 to 6 degrees), the laminitic foot is most easily diagnosed by the uneven HLZ, as there may be little else obvious (Figure 3).

Figure 3: Grade I laminitis with HLZ disparity.

The HLZ is the perpendicular distance between the hoof wall and the coffin bone. It is measured in two places, just below the extensor process and at the apex. The HLZ in adult light-breed horses is usually 17 to 19 mm (e.g., 17/17 mm, 18/18 mm, or 19/19 mm) (Figure 1). The more disparity between your first number and second number, the greater the laminar wedge or rotation away from your hoof wall. Note that an HLZ of greater than 20 mm in a light-breed horse represents serious edema.

The digital alignment, which is normally considered to be a straight line or 180 degrees when measured with a goniometer, will appear bent at the distal interphalangeal joint and will have a lower goniometer reading (e.g., 165 to 170 degrees). I like to measure the digital alignment from the dorsal distal face of P1 through the dorsal face of P2 and P3.

Grade II

Figure 4: Grade II with lamellar wedge.

A Grade II laminitic foot will have an increased palmar angle of 10 to 14 degrees. The disparity in the HLZ will be obvious, as will a decrease in the SDT measurement and an increase in both the EP/CB and SDW. The digital angle will be lower as well. A lamellar wedge is usually present on lateral radiographs (Figure 4).

Important ideas

Following are some important facts to keep in mind if you are fortunate enough to see a horse in the first stages of the disease process:

10 degrees of heel lift is always a good place to start, but then obtain radiographs and measurements and adjust the heel lift accordingly.

Always rasp the heels back from the quarters to the bulbs of the heels before applying a heel lift appliance.

Obtain lateral radiographs weekly, because a Grade I might become a Grade IV. Weekly radiographs will also help you determine if treatment is helping. The foot should grow 1 mm of sole a week. If the sole does not grow, it requires more help.

It takes six to eight weeks for the final pathology to demonstrate itself through radiographs.

Trying to figure out the mathematical needs of the foot is fun. Pull out a few old radiographs, judge the needs of those feet, and then look up your history to see what you did and how the horses responded. Grade I and II laminitis cases generally respond well to the therapy outlined here and should return to soundness, if treated properly.

Have fun with the calculations and maybe you will start enjoying these cases the way I did so many years ago.

Andrea E. Floyd, DVM, has specialized in equine podiatry for more than 25 years. She is the owner of Serenity Equine, Evington, Va., and the author of Equine Podiatry. Dr. Floyd is a member of the American Veterinary Medical Association, American Association of Equine Practitioners and the American Farriers Association.